1. Field
Embodiments of the present disclosure relate to a vacuum heat insulating material and a refrigerator including the same, and more particularly, to a vacuum heat insulating material having an improved structure to enhance the heat insulation efficiency.
2. Description of the Related Art
The energy consumed by human is limited, and global warming caused by carbon dioxide produced with the use of the energy is a problem which human confronts together with energy crisis. Accordingly, regulations of the energy consumption is getting tighten all over the world, and manufacturers of electric home appliances make efforts to comply with an energy consumption efficiency rating system of electric home appliances. The energy consumption efficiency rating system designed by the government to achieve the maximum efficiency with less energy suits for the demand of consumers who require high inner capacity and low power consumption. In particular, in the last several tens of years, many studies have been conducted on a refrigerator to reach the pinnacle in the studies associated with improving the efficiency of a cooling cycle, a compressor and a heat exchanger. Accordingly, in the recent years, studies have been mainly conducted on the heat loss, and various attempts have been made to enhance the energy efficiency by improving the heat insulating performance of the refrigerator.
The existing heat insulating material using polyurethane has a thermal conductivity of about 20 mW/(m*K), and the use of polyurethane heat insulating material makes the thickness of an outer wall of a refrigerator thicker, resulting in reduction of the storage capacity of the refrigerator. Accordingly, there is a need to use a vacuum heat insulating material having superior heat insulation efficiency.
The vacuum heat insulating material includes a core material and an envelope covering the core material. The envelope serves a great role to maintain the lifespan of the vacuum heat insulating material by blocking fine gas and vapor that infiltrate into the interior of a vacuum state. The envelope used for the vacuum heat insulating material is divided into an aluminum foil envelope and an aluminum deposition envelope. The aluminum foil envelope is obtained by attaching a PET film to an aluminum foil having a thickness of 5 μm or above and 12 μm or below. The aluminum deposition envelope is obtained by depositing aluminum on a PET film at a thickness of 15 μm or above and 100 nm or below, and then depositing the film having the aluminum deposited thereon in multi layers.
The thick aluminum layer of the aluminum foil envelope effectively blocks fine gas and vapor (moisture) of outside, and thus provides a superior durability. However, even if a central portion of the vacuum heat insulating material has a low thermal conductivity, a great amount of heat is exchanged through an edge portion. Such a phenomenon in which heat flows through an edge portion of the vacuum heat insulating material is referred to as the heat bridge.
Meanwhile, the aluminum deposition envelope has a thin aluminum layer and thus has a blocking efficiency of external fine gas and vapor (moisture) when compared to the aluminum foil envelope. In addition, as the aluminum deposition envelope is folded or bent in a process of manufacturing the aluminum deposition envelope, a fine pin hole is generated in the aluminum layer, and thus the durability of the aluminum envelope is lowered. However, the aluminum layer of the aluminum deposition envelope is thinner than that of the aluminum foil envelope, and thus the heat bridge does not occur.
As described above, there is a limitation to manufacture an effective vacuum heat insulating material since the aluminum foil envelope and the aluminum deposition envelope conflict with each in terms of the durability and the heat bridge.